(263a) High-Valent Redox Cathode Materials for Electrochemical Application

Advances in electrochemical devices such as batteries, fuel cells, and water-splitting membranes are making the global transition towards clean and renewable energy more possible than ever. Foundational to (electro)chemical and catalytic transformations in these devices are stable and reversible high-valent redox couples in mixed ionic-electronic conductors. In particular, the phenomenon of high-valent oxygen redox (anionic redox) in lithium- and sodium-ion positive electrodes has the potential to significantly improve cell energy density by providing additional high voltage capacity beyond that of most transition metal redox couples. However, the additional capacity from (anionic redox) has come at the expense of reduced reversibility in the form of voltage hysteresis and voltage fade. As a result, high valent redox couples have been historically avoided. In this talk, first, I will outline the mechanism and the framework for understanding the source of poor electrochemical reversibility in high-valent redox and the role defects play. Second, I will demonstrate a mechanism where structural disorder and voltage hysteresis can be completely avoided through defect engineering. Third, I will provide a set of actionable design rules involving tuning of defect formation energy landscape to engineer materials with high-valent redox couples for various applications.